Difference between revisions of "V9990"
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* Some registers have additional bits which are not documented. The mask describes which bits are read/write and which are unchanged. | * Some registers have additional bits which are not documented. The mask describes which bits are read/write and which are unchanged. | ||
Where the mask has a '1' bit, this bit is read/write. Where the mask has a '0' bit this bit remains at 0 and can't be changed. | Where the mask has a '1' bit, this bit is read/write. Where the mask has a '0' bit this bit remains at 0 and can't be changed. | ||
| + | - Register 7 (SCREEN MODE): Mask is &FF. | ||
- Register 9 (INTERRUPT READ/WRITE): Mask is &87 | - Register 9 (INTERRUPT READ/WRITE): Mask is &87 | ||
- Register 15 (BACK DROP COLOR): Mask is &FF | - Register 15 (BACK DROP COLOR): Mask is &FF | ||
Revision as of 09:05, 6 October 2018
- Reading from the Kanji ROM ports without a Kanji ROM returns databus values
- Palette index 0 has a mask of &9F (bits for r,g,b and color key), other indices have a mask of 0x01f for just r,g,b.
- If a command wants data written to the command port, you can't use a read, this will not clear the data request.
- If you read from a write-only register you will see data-bus value because the V9990 doesn't assert data on the bus.
- Some registers have additional bits which are not documented. The mask describes which bits are read/write and which are unchanged.
Where the mask has a '1' bit, this bit is read/write. Where the mask has a '0' bit this bit remains at 0 and can't be changed.
- Register 7 (SCREEN MODE): Mask is &FF. - Register 9 (INTERRUPT READ/WRITE): Mask is &87 - Register 15 (BACK DROP COLOR): Mask is &FF - Register 22 (SCROLL CONTROL): Mask is &C1 - Register 25 (SPRITE PATTERN GENERATOR TABLE BASE ADDRESS): Mask is &CF - Register 26 (LCD CONTROL): Mask is &FF - Register 27 (PRIORITY CONTROL): Mask is &FF
